Optical readers for scanning and decoding bar code symbols are generally known. A typical optical reader scanning system includes a light source, such as a laser, for providing a light beam; and an optical system for scanning the light beam in a predetermined pattern throughout a defined scanning region. In addition, the scanning system includes a detection system for detecting light having at least a predetermined intensity reflected from the bar code symbol and for providing an electrical signal in response to detection of such reflected light. Moreover, an optical system is included for directing light from the scanned light beam that is reflected from the bar code symbol to the detection system.
Recently, optical readers using one-dimensional and two-dimensional multi-photosensor array charge-coupled devices (CCDs) have become more and more prevalent. The multi-photosensor array CCDs are used to image an entire bar code symbol, and the resultant electronic image is then processed using pattern recognition techniques to decode the bar code symbol.
Both laser-based optical readers and CCD-based optical readers perform adequately. However, laser-based optical readers at times experience regulatory problems, can draw an unacceptable amount of electrical power and are subject to strict optical alignment requirements. CCD-based optical readers are at present still too expensive to enjoy widespread usage and have a very limited depth of field. The CCDs themselves are relatively expensive. In addition, significant computational power is required to decode in a timely manner.
In view of the aforementioned shortcomings associated with current optical readers, there is a strong need in the art for an optical reader which does not suffer from some of the same drawbacks as conventional optical readers. For example, there is a strong need in the art for an optical reader which does not require a laser or a CCD. Moreover, there is a strong need in the art for an image-based optical reader which is able to image and decode the bar code symbol even over a wide range of object distances between the optical reader and the bar code symbol.